Tire Pressure Monitoring Systems (TPMS) play an important role in vehicle safety and emissions reduction. A majority of this market is served by direct tire pressure monitoring systems, in which each tire contains a TPMS sensor module. Thus, a battery powered sensor module is assembled in the inside of a tire to monitor a tire pressure thereof. The sensor module contains a pressure sensor, a microcontroller, a radio-frequency (RF) transmitter and a coin battery cell. Principally, the sensor module measures the tire pressure and uses a unidirectional link to transmit the measurement data to a central unit in the vehicle. Since battery cannot be changed, sensor module lifetime is determined by battery lifetime. A major portion of the power consumption is generated by the RF transmission. Hence, it is an important task to reduce power consumption for RF transmission as much as possible.
For reducing power consumption of RF transmission two strategies exist: (1) choose a transmission interval as long as possible depending on situation (e.g., transmit every 10 minutes in parking but every 10 seconds while driving), or (2) only transmit when a change of pressure has been detected. The main problem with these strategies is the unidirectional link between tire module and vehicle control unit. In this case, the sensor module does not receive any feedback whether the transmitted data have been received or not. This is solved by transmitting data redundantly, e.g., repeating the telegram two or more times spaced by fixed and/or random pauses, without knowing whether a transmission has succeeded. The redundant transmissions increase power consumption considerably.
Therefore, an improved sensor module capable of reducing power consumption may be desirable.